10Factors Influencing the Intensity of S1Any condition that increases the force of ventricular contractionShortens, the PR intervalBrings the heart closer to the chest wall makes S1 louder (loud in children and young adults)When heart rate is normal, a loud S1 should alert the examiner of a possible short PR interval.Ventricular ContractilityPathological alteration of the cardiovascular system

11Ventricular ContractilityInfluence by the contractility of the Left Ventricle than by the Right VentricleEnhanced ContractilityS1 is accentuated (anemia, fever, pregnancy, exercise, anxiety)Poor ContractilityDecrease in the rate of pressure rise in the left ventricle, the first sound softens. (MI, cardiomypathies, shock)

12The PR Interval Reflects AV conduction timeThe time between atrial and ventricular contractionThe shorter the PR interval, the louder the first heart sound (mitral valve leaflets are wide open and deep within the ventricle when contraction begins causing the leaflets to close forcefully.The longer the PR interval, the softer the first soundThe PR interval directly influences the position of valve leaflets at the onset of ventricular systole

14Mitral StenosisMobile mitral cusp, one of the first and most consistent diagnostic clues is a typically loud and slapping heart sound.The loud S1 of mitral stenosis is caused by the closure of the mitral valve occurring on the steep upslope of the LV pressure curve during isometric contraction.Short PR interval

17Aortic Insufficiency S1 is diminished or absent in patientsMitral valve may be prematurely closed when systole begins because of a long PR interval or high LvedpPressures within the aorta a ventricle approach each other during diastole, isovolumic systole is either short or absent, causing a softening of S1

19Mitral Regurgitation S1 absent or weakValve leaflets may fail to seal the AV opening during ventricular systole because of structural defects or widening of the valve ring.Dissipation of LV pressure and the LADecrease in the rate of rise of LV pressure weakens the intensity of S1

20The heart has been sectioned to reveal the mitral valve as seen from above in the left atrium. The mitral valve demonstrates the typical "fish mouth" shape with chronic,

21Left Atrial MyxomaS1 is loud in patients with mobile myxoma of the LA because of a delay in mitral valve closureEchocardiography can provide a definitive diagnosisMechanism is similar to a short PR interval when the mitral leaflets are widely opened immediately before the onset of ventricular systole